Image coding system coding digital image signals by forming a histogram of a coefficient signal sequence to estimate an amount of information

Abstract

In an image coding system having a plurality of coding characteristics, such as quantization characteristics, information of a digital image signal sequence is monitored in each of a number of predetermined intervals by forming a histogram of a sequence of coefficients which is calculated from the digital image signal sequence in accordance with each of the coding characteristics. The amount of information is calculated by summing up the coefficients in relation to every one of the coding characteristics. An optimum one of the coding characteristics is indicated by the coding control circuit to code the coefficient sequence into a sequence of coded signals in accordance with the optimum coding characteristic. The coefficient sequence in each frame may be divided into a sequence of blocks each of which is judged to be either valid or invalid in relation to each coding characteristic. Results of judgement may be included in the amount of information.

What is claimed is: 
     
       1. In an image coding system for use in coding a sequence of digital image signals into a sequence of coded signals, said digital image signal sequence being divisible into predetermined intervals of time, said image coding system comprising dividing means responsive to said digital image signal sequence for dividing said digital image signal sequence into a sequence of blocks within each of said predetermined intervals, converting means coupled to said dividing means for successively carrying out predetermined conversion of the digital image signals of said blocks in each predetermined interval to produce a sequence of coefficient signals representative of coefficients resulting from said predetermined conversion, controllable coding means which has a plurality of coding characteristics and which is responsive to said coefficient signal sequence and to a characteristic selection signal for coding said coefficient signal sequence into said coded signal sequence in accordance with a selected one of said coding characteristics that is indicated by said characteristic selection signal, coding control means responsive to said coefficient signal sequence for producing a coding control signal determined in relation to an amount of information carried by said coefficient signal sequence, and supplying means for supplying said coding control signal to said controllable coding means as said characteristic selection signal, the improvement wherein said coding control means comprises: histogram forming means responsive to the coefficient signal sequence for forming a histogram representative of a distribution of said coefficients in each predetermined interval, said histogram forming means producing a histogram signal representative of said histogram; and   estimating means coupled to said histogram forming means and responsive to said histogram signal for estimating the amount of information carried by the coefficient signal sequence in every one of said predetermined intervals to produce, as said coding control signal, an estimation signal representative of a result of the estimation in every one of said predetermined intervals.   
     
     
       2. An image coding system as claimed in claim 1, wherein the blocks are divided into valid and invalid ones depending on whether coefficient signals representative of non-zero coefficients are contained in the coefficient signals of each block while the coefficient signals are also divided into valid and invalid ones depending on whether they represent non-zero coefficients, and wherein said histogram forming means comprises: first partial histogram forming means responsive to said coefficient signal sequence for forming a first partial histogram related to the valid and invalid ones of said blocks in every one of said predetermined intervals to produce a first partial histogram signal representative of said first partial histogram;   second partial histogram forming means responsive to said produce a second partial histogram signal representative of said second partial histogram; and   means for delivering said first and said second partial histogram signals as said histogram signal to said estimating means.   
     
     
       3. An image coding system as claimed in claim 2, wherein said controllable coding means comprises: quantization means which has a plurality of quantization characteristics as said plurality of coding characteristics, and which is responsive to said coefficient signal sequence and said estimation signal, said quantization means being for quantizing said coefficient signal sequence into a sequence of quantized signals in accordance with a selected one of said quantization characteristics indicated as said selected one of said coding characteristics by said estimation signal; and   variable length coding means coupled to said quantization means for carrying out variable length coding of said quantized signal sequence into said coded signal sequence.   
     
     
       4. In an image coding system for use in coding a sequence of digital image signals into a sequence of coded signals, said digital image signal sequence being divisible into predetermined intervals of time, said image coding system comprising dividing means responsive to said digital image signal sequence for dividing said digital image signal sequence into a sequence of blocks within each of said predetermined intervals, controllable coding means which has a plurality of coding characteristics and which is responsive to said digital image signal sequence and to a characteristic selection signal for coding said digital image signal sequence into said coded signal sequence in accordance with a selected one of said coding characteristics that is indicated by said characteristic selection signal, coding control means responsive to said digital image signal sequence for producing a coding control signal determined in relation to an amount of information carried by said digital image signal sequence, and supplying means for supplying said coding control signal to said controllable coding means as said characteristic selection signal, the improvement wherein said coding control means comprises: histogram forming means responsive to the digital image signal sequence for forming a histogram representative of a distribution of said digital image signals in each of said predetermined intervals, said histogram forming means producing a histogram signal representative of said histogram; and   estimating means coupled to said histogram forming means and responsive to said histogram signal for estimating the amount of information carried by the digital image signal sequence in every one of said predetermined intervals to produce, as said coding control signal, an estimation signal representative of a result of the estimation in every one of said predetermined intervals.   
     
     
       5. An image decoding system for use in combination with a coding system which produces a sequence of coded signals by dividing a sequence of digital image signals into a sequence of blocks in every one of predetermined intervals of time, by carrying out predetermined conversion of the digital image signals of the blocks in every one of said predetermined intervals into a sequence of coefficient signals which are representative of coefficients resulting from said predeterimined conversion, by forming a histogram representing an amount of information carried by said coefficient signal sequence and producing a histogram signal representative of said histogram, and by coding said coefficient signal sequence into said coded signal sequence in accordance with said histogram signal, said image decoding system comprising: decoding means for decoding said coded signal sequence into a reproduction of said coefficient signal sequence; and   inverse conversion means coupled to said decoding means for carrying out inverse conversion of said reproduction of said coefficient signal sequence relative to said predetermined conversion to produce a reproduction of said sequence of digital image signals.